Multi-spiral upset heat exchanger tube

ABSTRACT

A heat exchanger tube is provided that includes an inner diameter, an outer diameter and a longitudinal axis. The heat exchanger includes at least two spiral upsets protruding from the inner diameter of the tube and spiraling around the longitudinal axis of a length of the tube. The at least two spiral upsets include a first spiral upset having a cross-sectional shape, a depth of protrusion from the inner diameter, a pitch, and an angle with respect to the longitudinal axis, and a second spiral upset having a cross-sectional shape, a depth of protrusion from the inner diameter, a pitch, and an angle with respect to the longitudinal axis. In one embodiment, the angle of the first spiral upset with respect to the longitudinal axis is approximately equal to the angle of the second spiral upset with respect to the longitudinal axis, such that the first and second spiral upsets are approximately parallel. In another embodiment, the absolute value of the angle of the first spiral upset with respect to the longitudinal axis is different from the absolute value of the angle of the second spiral upset with respect to the longitudinal axis, such that the first and second spiral upsets intersect at least once. A method of manufacturing a heat exchanger tube is also provided.

FIELD OF THE INVENTION

The present invention relates generally to a heat exchanger tube andmore particularly to a heat exchanger tube having an inner diameter, anouter diameter, a longitudinal axis and at least two spiral upsetsprotruding from the inner diameter of the tube and spiraling around thelongitudinal axis of a length of the tube.

BACKGROUND

Heat transfer systems for cooling engine exhaust gases havetraditionally required relatively small amounts of heat transfer. Atypical engine exhaust gas cooling system is a shell-and-tube heatexchanger. A shell-and-tube heat exchanger includes a plurality of smalldiameter tubes (hereinafter heat exchanger tubes) that are encased in alarger diameter tube, providing a closed fluid flow passage. Theshell-and-tube heat exchanger is a preferred engine exhaust gas coolingsystem because of its relatively low cost and because it provides anadequate amount of heat transfer with a relatively small amount ofpressure drop in the fluid flowing therethrough.

A current heat exchanger tube for a shell-and-tube heat exchangerincludes an inner diameter having a plurality of rings protrudingtherefrom. The rings produce turbulence in the fluid flowing through thetube, which increases the heat transfer of the tube. However, the ringsproduce a significant reduction in the cross-sectional area of the tube,which increases the pressure drop in the fluid flowing through the tube.Another current heat exchanger tube for a shell-and-tube heat exchangerincludes an inner diameter having a single spiral protruding therefrom.The spiral produces less of a reduction in the cross-sectional area ofthe tube, and therefore less of a pressure drop in the fluid flowingthrough the tube. However, the spiral also produces less turbulence inthe fluid flowing through the tube and therefore provides less heattransfer in the tube.

Accordingly, a need exists for a heat exchanger tube for ashell-and-tube heat exchanger that provides a large amount of heattransfer without significantly increasing the pressure drop of the fluidflowing through the tube.

SUMMARY

In one embodiment, the present invention is a heat exchanger tube havingan inner diameter, an outer diameter and a longitudinal axis. The heatexchanger includes at least two spiral upsets protruding from the innerdiameter of the tube and spiraling around the longitudinal axis of alength of the tube. The at least two spiral upsets include a firstspiral upset having a cross-sectional shape, a depth of protrusion fromthe inner diameter, a pitch, and an angle with respect to thelongitudinal axis, and a second spiral upset having a cross-sectionalshape, a depth of protrusion from the inner diameter, a pitch, and anangle with respect to the longitudinal axis, wherein the angle of thefirst spiral upset with respect to the longitudinal axis isapproximately equal to the angle of the second spiral upset with respectto the longitudinal axis, such that the first and second spiral upsetsare approximately parallel.

In another embodiment, the absolute value of the angle of the firstspiral upset with respect to the longitudinal axis is different from theabsolute value of the angle of the second spiral upset with respect tothe longitudinal axis, such that the first and second spiral upsetsintersect at least once.

In yet another embodiment, the present invention is a method ofmanufacturing a heat exchanger tube. The method includes providing atube having an inner diameter, an outer diameter and a longitudinalaxis. The method also includes providing at least two spiral upsetsprotruding from the inner diameter of the tube and spiraling around thelongitudinal axis of a length of the tube. Providing the at least twospiral upsets includes providing a first spiral upset having across-sectional shape, a depth of protrusion from the inner diameter, apitch, and an angle with respect to the longitudinal axis, and providinga second spiral upset having a cross-sectional shape, a depth ofprotrusion from the inner diameter, a pitch, and an angle with respectto the longitudinal axis, wherein the angle of the first spiral upsetwith respect to the longitudinal axis is approximately equal to theangle of the second spiral upset with respect to the longitudinal axis,such that the first and second spiral upsets are approximately parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a heat exchanger tube according to oneembodiment of the present invention;

FIG. 2 is a perspective view of a heat exchanger tube according toanother embodiment of the present invention;

FIG. 3 is a perspective view of a heat exchanger tube according to yetanother embodiment of the present invention;

FIG. 4 is a radial cross-sectional view taken from line 4-4 of FIG. 2;

FIG. 5 is a radial cross-sectional view of one embodiment of the presentinvention;

FIG. 6 is a radial cross-sectional view of another embodiment of thepresent invention;

FIG. 7 is a radial cross-sectional view of yet another embodiment of thepresent invention; and

FIG. 8 is a radial cross-sectional view of still another embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As shown in FIGS. 1-8, embodiments of the present invention are directedto a heat exchanger tube having an inner diameter, an outer diameter, alongitudinal axis, and at least two spiral upsets protruding from theinner diameter of the tube and spiraling around the longitudinal axis ofa length of the tube. The multi-spiral upset heat exchanger tube of thepresent invention produces turbulence in the fluid flowing therethroughrather than the rifling or swirling effect that a single spiral upsetheat exchanger tube produces. In addition, the multi-spiral upset heatexchanger tube of the present invention produces turbulence withoutsignificantly reducing the cross-sectional area of the tube as ringedheat exchanger tubes do. As a result, the multi-spiral upset heatexchanger tube of the present invention produces a large amount of heattransfer without significantly increasing the pressure drop of the fluidflowing through the tube.

FIGS. 1-3 show embodiments of a multi-spiral upset heat exchanger tube10 according to the present invention. The tube 10 includes an innerdiameter 12, an outer diameter 14 and a longitudinal axis 16. The tube10 also includes at least two spiral upsets protruding from the innerdiameter 12 of the tube 10 and spiraling around the longitudinal axis 16of a length of the tube 10. In one embodiment, the tube 10 includes afirst spiral upset 18 and a second spiral upset 20. The first spiralupset 18 includes a cross-sectional shape 18S, a depth of protrusion 18Dfrom the inner diameter 12, a pitch 18P, and an angle ∀ with respect tothe longitudinal axis 16, and second spiral upset 20 includes across-sectional shape 20S, a depth of protrusion 20D from the innerdiameter 12, a pitch 20P, and an angle ∃ with respect to thelongitudinal axis 16, wherein pitch is defined as a longitudinaldistance traveled by a spiral in a single revolution.

In the embodiment depicted in FIG. 1, the angle ∀ of the first spiralupset 18 with respect to the longitudinal axis 16 is approximately equalto the angle ∃ of the second spiral upset 20 with respect to thelongitudinal axis 16, such that the spiral upsets 18 and 20 areapproximately parallel.

In the embodiments depicted in FIGS. 2 and 3, the angle ∀ of the firstspiral upset 18 with respect to the longitudinal axis 16 is differentfrom the angle ∃ of the second spiral upset 20 with respect to thelongitudinal axis 16, such that the spiral upsets 18 and 20 intersect atleast once. The angles ∀ and ∃ of the first and second spiral upsets 18and 20 with respect to the longitudinal axis 16 may be different buthave the same absolute value (as shown in FIG. 2) or the angles ∀ and ∃may be different and have different absolute values (as shown in FIG.3).

The spiral upsets 18 and 20 may spiral in the same direction or inopposite directions. For example, in the embodiment depicted in FIG. 2,the spiral upsets 18 and 20 spiral in opposite directions, that is theangle ∀ of the first spiral upset 18 with respect to the longitudinalaxis 16 is smaller than 90°, such that the first spiral upset 18 spiralsin a clockwise direction and the angle ∃ of the second spiral upset 20with respect to the longitudinal axis 16 is larger than 90°, such thatthe second spiral upset 20 spirals in a counter-clockwise direction.

In the embodiments depicted in FIGS. 1 and 3, the spiral upsets 18 and20 spiral in the same direction, that is the angles ∀ and ∃ of thespiral upsets 18 and 20, respectively, with respect to the longitudinalaxis 16 are each smaller than 90°, such that the spiral upsets 18 and 20each spiral in a clockwise direction. In another embodiment, the angles∀ and ∃ of the spiral upsets 18 and 20, respectively, with respect tothe longitudinal axis 16 are each larger than 90°, such that the spiralupsets 18 and 20 each spiral a counter-clockwise direction.

In general the closer the angles ∀ and ∃ of the spiral upsets 18 and 20are to 90°, the greater the turbulence and pressure drop of the fluidflowing through the tube 10. The increase in turbulence of the fluidflowing through the tube 10 increases the heat transfer of the tube 10,but also increases the pressure drop of the fluid flowing through thetube 10. As a result, in this and in other embodiments described below atrade off exists between increasing heat transfer of the tube 10 andincreasing the pressure drop of the fluid flowing through the tube 10.This should be taken into account when designing the tube 10 for aspecific heat transfer requirement at a specific pressure drop limit.

In any of the embodiments described above, the cross-sectional shapes18S and 20S of the spiral upsets 18 and 20, respectively, may bedifferent or approximately the same. FIGS. 4-8 show various appropriatecross-sectional shapes for the spiral upsets. For example, thecross-sectional shape of each spiral upset may be semi-circular (FIG.4), semi-rectangular (FIG. 5), poly-sided such as a semi-hexagon (FIG.6), V-shaped (FIG. 7), or U-shaped (FIG. 8), among other appropriatecross-sectional shapes.

In general, the greater the surface area of the cross-sectional shapes18S and 20S of the spiral upsets 18 and 20, respectively, the greaterthe turbulence and pressure drop of the fluid flowing through the tube10. Also, when the cross-sectional shapes 18S and 20S are different, theturbulence and pressure drop of the fluid flowing through the tube 10are increased and in general, the greater the difference in shape and/orsize of the cross-sectional shapes 18S and 20S of the spiral upsets 18and 20, the greater the turbulence and pressure drop of the fluidflowing through the tube 10.

In any of the embodiments described above, the depths 18D and 20D of thespiral upsets 18 and 20, respectively, may be different or approximatelythe same. In general, the greater the depths 18D and 20D of the spiralupsets 18 and 20, the greater the turbulence and pressure drop of thefluid flowing through the tube 10. Also, when the depths 18D and 20D ofthe spiral upsets 18 and 20 are different, the turbulence and pressuredrop of the fluid flowing through the tube 10 are increased and ingeneral, the greater the difference in the depths 18D and 20D of thespiral upsets 18 and 20, the greater the turbulence and pressure drop ofthe fluid flowing through the tube 10.

In any of the embodiments above, the pitches 18P and 20P of the spiralupsets 18 and 20 may be different or approximately equal. When thepitches 18P and 20P are approximately equal, the first and second spiralupsets 18 and 20 intersect exactly once per revolution. When the pitches18P and 20P are different, the first and second spiral upsets 18 and 20intersect more than once per revolution. For example, when the pitch 18Pof the first spiral upset 18 is twice as long as the pitch 20P of thesecond spiral upset 20, the first spiral upset 18 intersects the secondspiral upset 20 twice per revolution. In general, the more intersectionsbetween the spiral upsets 18 and 20 per revolution, the greater theturbulence and pressure drop of the fluid flowing through the tube 10.Also in general, any change in the pitch of a spiral upset effects theangle of the spiral upset with respect to the longitudinal axis of thetube and vice versa.

As can be seen above, the number of embodiments of the multi-spiralupset heat exchanger tube 10 according to the present invention can bevaried extensively by varying:

-   -   the angles ∀ and ∃ of the spiral upsets 18 and 20 with respect        to the longitudinal axis 16 of the tube 10;    -   varying the cross-sectional shapes 18S and 20S of the spiral        upsets 18 and 20;    -   varying the depths 18D and 20D of the spiral upsets 18 and 20;    -   varying the pitches 18P and 20D of the spiral upsets 18 and 20;    -   providing equal or unequal angles ∀ and ∃ of the spiral upsets        18 and 20 with respect to the longitudinal axis 16 of the tube        10;    -   spiraling the spiral upsets 18 and 20 in the same or opposite        directions;    -   providing different or approximately the same cross-sectional        shapes 18S and 20S;    -   providing different or approximately the same depths 18D and        20D; and    -   providing different or approximately the same pitches 18P and        20D.

As a result, the multi-spiral upset heat exchanger tube 10 according tothe present invention allows for a greater adjustability of theturbulence and pressure drop of the fluid flowing through the tube 10than that which is provided by ringed heat exchanger tubes and singlespiral heat exchanger tubes. Therefore, when a system requires aspecific amount of heat transfer at a specific pressure drop limit, thevariable described above can be adjusted to meet the specific givenrequirements.

For example, in one embodiment the tube 10 includes spiral upsets 18 and20 that intersect at least once, have angles ∀ and ∃ with respect to thelongitudinal axis 16 that are close to 90°, have depths of protrusion18D and 20D that are relatively large, and have cross-sectional shapes18S and 20S with relatively large surface areas. This embodimentproduces a tube 10 with a relatively large amount of heat transfer. Inanother embodiment, the tube 10 includes spiral upsets 18 and 20 thatare parallel, have angles ∀ and ∃ with respect to the longitudinal axis16 that are close to 0°, have depths of protrusion 18D and 20D that arerelatively small, and have cross-sectional shapes 18S and 20S withrelatively small surface areas. This embodiment produces a tube with arelatively small amount of heat transfer.

The multi-spiral upset heat exchanger tube 10 according to the presentinvention may be composed of any one of a variety of materials. Forexample, the tube 10 may be composed of a metal material, such asstainless steel, aluminum, or copper, among other appropriate materials.In addition, the tube 10 may be manufactured by any one of a variety ofmethods, such as machining, casting, or extruding. For example, in amachining operation, the tube 10 may be manufactured by rotating amandrel with respect to the tube 10 to produce spiraled grooves thatform the first and second spiral upsets 18 and 20 in the tube 10.

Although the above description and the accompanying figures describe themulti-spiral upset heat exchanger tube 10 as having two spiral upsets 18and 20, the tube may have any greater number of spiral upsets.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Persons skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structures and methods ofoperation can be practiced without meaningfully departing from theprinciple, spirit and scope of this invention. Accordingly, theforegoing description should not be read as pertaining only to theprecise structures described and shown in the accompanying drawings, butrather should be read as consistent with and as support for thefollowing claims, which are to have their fullest and fairest scope.

1. A heat exchanger tube comprising: an inner diameter, an outerdiameter and a longitudinal axis; and at least two spiral upsetsprotruding from the inner diameter of the tube and spiraling around thelongitudinal axis of a length of the tube, wherein the at least twospiral upsets comprise: a first spiral upset having a cross-sectionalshape, a depth of protrusion from the inner diameter, a pitch, and anangle with respect to the longitudinal axis, and a second spiral upsethaving a cross-sectional shape, a depth of protrusion from the innerdiameter, a pitch, and an angle with respect to the longitudinal axis,wherein the angle of the first spiral upset with respect to thelongitudinal axis is approximately equal to the angle of the secondspiral upset with respect to the longitudinal axis, such that the firstand second spiral upsets are approximately parallel.
 2. The heatexchanger tube claim 1, wherein the cross-sectional shape of the firstspiral upset is approximately the same as the cross-sectional shape ofthe second spiral upset.
 3. The heat exchanger tube claim 1, wherein thecross-sectional shape of the first spiral upset is different from thecross-sectional shape of the second spiral upset.
 4. The heat exchangertube claim 1, wherein the cross-sectional shape of the first spiralupset is chosen from the group consisting of semi-circular,semi-rectangular, poly-sided, V-shaped and U-shaped and thecross-sectional shape of the second spiral upset is chosen from thegroup consisting of semi-circular, semi-rectangular, poly-sided,V-shaped and U-shaped.
 5. The heat exchanger tube claim 1, wherein thedepth of protrusion of the first spiral upset from the inner diameter ofthe tube is approximately equal to the depth of protrusion of the secondspiral upset from the inner diameter of the tube.
 6. The heat exchangertube claim 1, wherein the depth of protrusion of the first spiral upsetfrom the inner diameter of the tube is different from the depth ofprotrusion of the second spiral upset from the inner diameter of thetube.
 7. The heat exchanger tube claim 1, wherein the pitch of the firstspiral upset is approximately equal to the pitch of the second spiralupset.
 8. The heat exchanger tube claim 1, wherein the pitch of thefirst spiral upset is different from the pitch of the second spiralupset.
 9. The heat exchanger tube claim 1, wherein the cross-sectionalshape of the first spiral upset is different from the cross-sectionalshape of the second spiral upset, wherein the depth of protrusion of thefirst spiral upset from the inner diameter of the tube is different fromthe depth of protrusion of the second spiral upset from the innerdiameter of the tube, and wherein the pitch of the first spiral upset isdifferent from the pitch of the second spiral upset.
 10. A heatexchanger tube comprising: an inner diameter, an outer diameter and alongitudinal axis; and at least two spiral upsets protruding from theinner diameter of the tube and spiraling around the longitudinal axis ofa length of the tube, wherein the at least two spiral upsets comprise: afirst spiral upset having a cross-sectional shape, a depth of protrusionfrom the inner diameter, a pitch, and an angle with respect to thelongitudinal axis, and a second spiral upset having a cross-sectionalshape, a depth of protrusion from the inner diameter, a pitch, and anangle with respect to the longitudinal axis, wherein the absolute valueof the angle of the first spiral upset with respect to the longitudinalaxis is different from the absolute value of the angle of the secondspiral upset with respect to the longitudinal axis, such that the firstand second spiral upsets intersect at least once.
 11. The heat exchangertube claim 10, wherein the angle of the first spiral upset with respectto the longitudinal axis is smaller than 90° and the angle of the secondspiral upset with respect to the longitudinal axis is larger than 90°,such that the first and second spiral upsets spiral in oppositedirections, that is, the first spiral upset spirals in a clockwisedirection and the second spiral upset spirals in a counter-clockwisedirection.
 12. The heat exchanger tube claim 10, wherein thecross-sectional shape of the first spiral upset is approximately thesame as the cross-sectional shape of the second spiral upset.
 13. Theheat exchanger tube claim 10, wherein the cross-sectional shape of thefirst spiral upset is different from the cross-sectional shape of thesecond spiral upset.
 14. The heat exchanger tube claim 10, wherein thecross-sectional shape of the first spiral upset is chosen from the groupconsisting of semi-circular, semi-rectangular, poly-sided, V-shaped andU-shaped and the cross-sectional shape of the second spiral upset ischosen from the group consisting of semi-circular, semi-rectangular,poly-sided, V-shaped and U-shaped.
 15. The heat exchanger tube claim 10,wherein the depth of protrusion of the first spiral upset from the innerdiameter of the tube is approximately equal to the depth of protrusionof the second spiral upset from the inner diameter of the tube.
 16. Theheat exchanger tube claim 10, wherein the depth of protrusion of thefirst spiral upset from the inner diameter of the tube is different fromthe depth of protrusion of the second spiral upset from the innerdiameter of the tube.
 17. The heat exchanger tube claim 10, wherein thepitch of the first spiral upset is approximately equal to the pitch ofthe second spiral upset.
 18. The heat exchanger tube claim 10, whereinthe pitch of the first spiral upset is different from the pitch of thesecond spiral upset.
 19. The heat exchanger tube claim 10, wherein thecross-sectional shape of the first spiral upset is different from thecross-sectional shape of the second spiral upset, wherein the depth ofprotrusion of the first spiral upset from the inner diameter of the tubeis different from the depth of protrusion of the second spiral upsetfrom the inner diameter of the tube, and wherein the pitch of the firstspiral upset is different from the pitch of the second spiral upset. 20.A method of manufacturing a heat exchanger tube comprising: providing atube having an inner diameter, an outer diameter and a longitudinalaxis; and providing at least two spiral upsets protruding from the innerdiameter of the tube and spiraling around the longitudinal axis of alength of the tube, wherein providing the at least two spiral upsetscomprises: providing a first spiral upset having a cross-sectionalshape, a depth of protrusion from the inner diameter, a pitch, and anangle with respect to the longitudinal axis, and providing a secondspiral upset having a cross-sectional shape, a depth of protrusion fromthe inner diameter, a pitch, and an angle with respect to thelongitudinal axis, wherein the angle of the first spiral upset withrespect to the longitudinal axis is approximately equal to the angle ofthe second spiral upset with respect to the longitudinal axis, such thatthe first and second spiral upsets are approximately parallel.